This invention relates to a fuse-containing semiconductor device. Recently it has been common practice to build a fuse into a semiconductor device. This procedure arises from the requirements of writing data in a ROM unit by melting away the fuse; or protecting the predetermined element or elements involved in a semiconductor device, or exchanging spare bits provided in a RAM unit. The sectional view of FIG. 2 illustrates the arrangement of a fuse built in the above-mentioned type of semiconductor device. Referring to FIG. 2, insulating layer 4 is deposited on a silicon semiconductor substrate 1. Further, fuse 7 is mounted on the insulating layer 4. Fuse 7 is connected to first wiring 6 at one end, and to second wiring 8 at the other end.
Since fuse 7 has a relatively high resistance of about 10 .OMEGA., the customary practice is to provide a thin polycrystalline silicon layer adjusted to have a sheet resistance of about 40 .OMEGA./.quadrature. by impurity doping and trimming the thin polycrystalline layer so as to let it have a width of 10 microns and a length of about 3 microns (Japanese patent disclosure Sho No. 59-130441). Fuse 7 is prepared from a thin aluminium film, which is deposited on insulating layer 4. The aluminium layer is irradiated by laser beams in order to be converted into Al.sub.2 O.sub.3, thereby controlling the sheet resistance to a predetermined level (Japanese patent disclosure Sho No. 60-84835).
Since, in recent years, semiconductor elements involved in a semiconductor device have been progressively miniaturized, fusion current has also decreased in magnitude. Consequently, the fuse built in a semiconductor device must have the following features: fuse resistance below 5 .OMEGA.; fusion current of a lower magnitude than 0.5 A, and fusion completed within 30 seconds.
However, the conventional fuse prepared from polycrystalline silicon presents difficulties in realizing a low resistance of less than 5 .OMEGA./.quadrature.. Even if such a low resistance could be attained, the problem arose that the aluminium component of the aluminium electrode connected to the fuse tended to diffuse into the polycrystalline silicon constituting the fuse, thus undesirably giving rise to changes in the properties of the fuse, such as its electric resistance and fusion feature. An aluminum fuse can indeed have its resistance easily reduced to a lower level than 5 .OMEGA.. However, the fusion current, if set at a lower level than 0.5 A, will become extremely unstable. Namely, some fuses melt within 30 seconds, while other fuses consume 90 seconds in completing melting.